Positioning possibilities within wireless communication networks play an important role in modern communication systems and will probably be even more exploited in future development. Applications, such as emergency call positioning, position-supported services etc. now form a compulsory part of any modern cellular communication system. Many different kinds of information available in different nodes can be utilized for positioning purposes. In order to be able to perform position determinations, positioning information of different types has to be communicated between different nodes in a communication system as well as different types of instructions and orders. The reporting procedures for positioning-related information therefore also play an important role in the communication systems.
Many different positioning approaches are used today. Cell ID positioning is based on the geometrical area of a cell in which a User Equipment (UE) is situated. In Round Trip Time (RTT) positioning, the time of a radio signal to travel forth and back between a base station and a UE is measured and a distance between the base station and the UE can be computed. In Observed Time Difference Of Arrival (OTDOA), time differences between signals from a multiple of transmit points are used for triangulation purposes. In positioning with an Assisted Global Positioning System (A-GPS), which is an enhancement of the Global Positioning System (GPS), GPS receivers in terminals connected to the cellular communication system, enhance the performance of the GPS UE receivers. The Adaptive Enhanced Cell-ID (AECID) method is an enhanced fingerprinting positioning method, where databases with collected high precision positions associated with a number of radio properties, cell IDs, RTT measurements and/or received signal strengths, are used for positioning purposes. A-UPS can by advantage be used for determine such high precision positions. However, A-UPS has a limited availability indoors.
Another method that can serve for achieving a high-precision positioning measurement is Uplink Time Difference Of Arrival (UTDOA) positioning. A multiple of receiving points at different locations, typically Radio Base Stations (RBS) or Location Measurement Units (LMU), receive the same radio signal. By combining differences in arrival times, a relatively precise position may be determined.
The UTDOA method belongs to the set of high precision methods. The inaccuracy is, however, significantly larger than that of A-GPS. The main advantage of UTDOA is that it provides high precision positioning also indoors, a situation where the availability of A-GPS is very limited.
To perform UTDOA timing measurements also on user data, to increase the signal to noise ratio, one reference receiver de-codes the UE signals, and forwards the sequence to cooperating receivers. This procedure is relatively complex and requires a significant amount of signaling. The cooperating receivers are normally located in dedicated hardware close to the positioning node. The decoded reference sequence is used in order to regenerate the transmitted sequence from the UE to allow correlation against each forwarded received set of data from the involved receivers in different locations (typically RBS locations).
The main problem with all terrestrial time difference of arrival positioning methods is to detect/be detected in a sufficient number of non-co-located locations. In the case of UTDOA, the problem consists of detection of the same UE transmission in a sufficient number of RBSs base stations (assuming that UTDOA timing measurements are performed in connection to RBSs). This is in general a difficult problem since it requires a sufficiently high signal-to-noise ratio in a number of locations, sometimes far away from the UE. It needs to be noted that the theoretical minimum of three neighbor locations is typically not enough in practice in many situations the number of neighbors may be twice this figure to obtain a reliable performance.
Similar requirements and problems are also present in other types of uplink positioning measurements, such as Time Of Arrival (TOA), Time Difference Of Arrival (TDOA) or signal strength measurements.
In many modern cellular communication systems of today, different carriers are available in one and the same cell. In Wideband Code Division Multiple Access (WCDMA) systems, the Universal mobile telecommunication system Terrestrial Radio Access Network (UTRAN) may redirect the UE to another frequency. The UE autonomously selects a carrier, in 3GPP specifications referred to as “cell reselection”, and signals the selected carrier according to a specified “cell update” procedure.
Dual-Carrier High-Speed Downlink Packet. Access (DC-HSDPA) was introduced within the 3rd Generation Partnership Project (3GPP) Rel-8. DC-HSDPA enables reception of data from two cells simultaneously, transmitted on two adjacent carriers in the same radio base station and sector, to individual terminals or UE. The concept of DC-HSDPA is in 3GPP Rel-10, extended to 4 downlink carrier frequencies (known as 4C-HSDPA).
To complement DC-HSDPA, in 3GPP Rel-9, Dual-Carrier High-Speed Uplink Packet Access (DC-HSUPA) was also introduced. DC-HSUPA enables an individual terminal to transmit data on two adjacent carrier frequencies simultaneously to the radio access network. DC-HSUPA according to 3GPP Rel-9 is in essence an aggregation of legacy (Rel-8, single-carrier) HSUPA.
The following problems with prior art technology can be noted for uplink positioning. Note also that Long-Term Evolution (LTE) uplink positioning, and in particular UTDOA, has not even been standardized yet. In case several carriers are available in an RBS, it is not known in the positioning node, e.g. situated in a Radio Network Controller (RNC) or a Stand-Alone Serving Mobile Location Centre (SAS) node, on which carrier, if any, uplink measurement reference and slave receivers are available for. Note that uplink positioning measurements are normally performed in separate hardware. Therefore it is not evident for which carriers this is possible. In general, more carriers results in a more expensive radio. In one example, single-carrier measurement units e.g. LMUs), which are either configured for the single-carrier operation on a certain carrier or simply do not support multi-carrier operation mode, may operate in a multi-carrier network. The positioning nodes have today no possibilities to influence which uplink carrier to be used by the UE.
The uplink positioning requires as mentioned above that a sufficiently high signal-to-noise ratio is available at a sufficient number of detection locations. The reference receiver must be able to detect and possibly decode, e.g. for further regeneration, the measurement signal with a very high likelihood. In case more than one carrier is possible to use, one or several carriers may have sufficient signal-to-noise ratios for enabling uplink positioning, while one or several carriers may have to noisy conditions. Today, there are no possibilities for the positioning node to judge which carriers are at all useful and which are not.